CAIE Biology IGCSE Summary Notes 2: Organisation of the Organism PDF

CAIE Biology IGCSE 2: Organisation of the Organism Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0...

CAIE Biology IGCSE 2: Organisation of the Organism Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Cell Structure Comparing the structure of animal cells and plant cells: Similarities: They both contain a nucleus, cytoplasm, mitochondria, ribosomes and a cell membrane. Differences: Plant cells contain a cell wall, vacuole and chloroplasts. Plant cells have a more regular shape and are larger. Animal cells Plant cells https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Functions of cell structures in animal and plant cells: Cytoplasm - A jelly-like material within the cell in which reactions occur. The cytoplasm contains structures such as ribosomes and vesicles. Cell membrane - a thin membrane that surrounds the cell, controls entry and exit of substances. Nucleus - the nucleus contains genetic material in the form of DNA which codes for proteins. DNA replication also occurs in the nucleus. Ribosomes - Ribosomes are the site of protein synthesis. Mitochondria - site of respiration. Provides energy for the cell to function. In plants only: Vacuole - is a fluid-filled sac containing mineral salts, sugars, amino acids, waste substances and pigments which colour the cell and attract pollinating insects. Chloroplasts - the site of photosynthesis, which allows plants to convert light energy to glucose. Cell wall - gives the cell structure and prevents bursting. It is made of cellulose. Bacterial cells: Bacterial cells contain a cell wall, cell membrane, cytoplasm and ribosomes. The cell wall of a bacterial cell is made of a different material than in plant cells. This material is called peptidoglycan. Bacterial cells do not have a nucleus but instead contain circular DNA - a loop of DNA which floats in the cytoplasm. The circular DNA contains most of the genetic material in the cell. These cells also lack mitochondria and chloroplasts. Bacterial cells contain plasmids. Plasmids are small rings of DNA. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc New cells are produced by the division of existing cells. Specialised cells: Cells and tissues are specialised to carry out their particular function. Examples of specialised cells are: Ciliated cells - ciliated cells are found lining the trachea. They have hair-like projections called cilia which move together to transport mucus, dust and bacteria upwards to the throat. Root hair cells - are adapted to have a large surface area. This speeds up the rate of osmosis and mineral ion uptake in plants. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Palisade mesophyll cells - this is where photosynthesis occurs. Mesophyll cells are tall and closely packed to efficiently absorb light and contain lots of chloroplasts for photosynthesis. They are also placed at the top of the leaf where most of the light hits, enabling them to absorb as much light energy as possible. Neurones - nerve cells are adapted to rapidly transmit electrical impulses. Nerve cells are myelinated, which insulates the cell and prevents the impulse weakening and slowing down. They also contain lots of mitochondria to provide energy. Dendrites have a large surface area and are branched to receive impulses from many other neurons. Red blood cells - red blood cells contain haemoglobin which allows them to carry oxygen around the body. They have a biconcave shape which increases their surface area, allowing for rapid diffusion. They also have thin cell membranes to decrease the diffusion distance. They do not contain a nucleus, thus have more space for oxygen. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Sperm cells - sperm cells are gametes. Gametes are the reproductive cells of organisms with half the chromosomes of normal cells. Sperm cells are adapted by containing lots of mitochondria so that the cell has enough energy to reach the egg cell. It has a tail to allow movement and contains digestive enzymes to help penetrate the egg cell membrane. Egg cells - egg cells are also gametes. Egg cells have nutrients in their cytoplasm which help the growth of the embryo. After fertilisation, the cell membrane changes to prevent any more sperm from penetrating the egg. Egg cells are haploid, meaning they contain only half the number of chromosomes of normal cells. Thus, when the sperm fertilises the egg cell, the embryo will have the right number of chromosomes. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Levels of organisation: Key terms: Cell - the basic building block of all living organisms Tissue - a group of similar cells working together to carry out a particular process Organ - a group of tissues working together to carry out a specific function Organ system - a group of related organs working together to carry out functions in the body. Size of specimens Cells can be viewed using a microscope to study their structure. To calculate the size of a specimen under a microscope, we use the following formula: Where the image size is the size of the specimen which appears when viewed through the microscope. The actual size is the specimen’s real size. The image size should be measured in millimetres. Example: A student measures the image of a cell under a microscope and it is 32mm wide. The image has been magnified by a factor of x 100. What is the actual width? Using the formula above: Actual size = Image size / Magnification 32/100 = 0.32 mm https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc You may be asked to give the answer in micrometres. To convert between millimetres and micrometres, you need to multiply by 1000. 1mm = 1000 µm µm is the symbol used to represent micrometres. Example: A student measures the image of a cell under a microscope and it is 54mm wide. The image has been magnified by a factor of x 500. What is the actual width in µm? Actual size = Image size / Magnification 54/500 = 0.108 mm 0.108 mm x 1000 = 108 µm Actual width = 108 µm https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc